The noisy buzz of the mains electricity power supply has been one of our urban environment’s most persistent background noises. One day in 1996 Dr Catalin Grigoras realised that the electricity wasn't just making noise, but in fact singing...

The UK national electrical grid delivers power across the country. This mains power supply makes a constant humming sound, yet there are tiny changes to the frequency of this sound every second. Most recordings made in the UK have a trace of mains hum on them and this can be forensically analysed to determine the time and date they were made, and as a result, whether anyone has edited the recording.

For over ten years, the UK government has used this technique as a surveillance tool. This is the Hummingbird Clock, an online time piece that aims at making this technique available to everyone. If you need to know the exact time an audio or video recorded event took place in the UK after 7 July 2016 then simply submit a claim.